1. Field of the Invention
The present invention relates generally to serial bus networks, and more specifically to a standardized serial bus network such as IEEE Std 1394-1995 or IEEE Std 1394a-2000 (hereinafter IEEE 1394 standard) in which bus bridges are used to interconnect serial buses and TCP/IP protocol is used for inter-bridge communications.
2. Description of the Related Art
Recent attentions have increasingly been focused on the high speed transport capability of the IEEE 1394 serial bus network to promote multimedia communications. One such effort has culminated in the IP over IEEE 1394 protocol (RFC 2734) developed by the IETF (Internet Engineering Task Force) to support the Internet Protocol. The IP over IEEE 1394 protocol defines a method in which IP packets are transmitted in unicast, multicast and broadcast modes. According to the IP over IEEE 1394 protocol, “asynchronous packets” are used for transmitting unicast messages and “asynchronous stream channels” are used for transmitting multicast and broadcast messages. Multicast channel allocation protocol is also defined for allocating an asynchronous stream channel to a number of nodes attached to a common bus.
The Serial Bus architecture supports multiple bus networks via bus bridges. A bus bridge normally eavesdrops on the bus, ignoring all transactions between local addresses but listening for remote transactions. When the bus bridge receives a packet for a remote address, it forwards the packet to an adjacent bus. After initialization, the bus bridges are transparent to the system. Bus bridges are also used to segment a large system into a number of small bus systems.
However, the multicast channel allocation protocol limits the reachable extent of multicast transmissions to only one bus system. While unicast and broadcast messages can be transmitted between multiple bus system via bus bridges, the bus bridges allow no inter-bridge multicast transmissions.
Therefore, there exists a need to provide bus bridges capable of retransmitting multicast packets from a multicast group of one bus system to a multicast group of another bus system. If a multiple bus network has three or more bus systems, intermediate bus systems must be capable of acquiring an asynchronous stream channel for retransmitting multicast messages from source to destination bus systems. In addition, such intermediate bus systems must also be capable of acquiring an asynchronous stream channel for multicast transmission even if their nodes are all receive-only nodes which are currently not designed to acquire an asynchronous stream channel.